"implement the processing" or "implement a procedure for processing"?

I personally would favour the latter because the indefinite article in the French is not necessarily insignificant. It's shades of meaning, but the French makes clear that there is no one specific way to do this.

I think the two previous answers are too literal and cumbersome. You have to paraphrase, avoid the repetition of "processing" in the French, and include the word "controller" from the GDPR.

I suggest

The organiser processes personal data concerning (competition) entrants, and is the controller of that data (as defined in the GDPR)

You could add the bit in brackets if you feel it's necessary.

It's with respect to work and the duties surrounding data:
"The organizer makes use of such while being responsible for guarding or the preservation of confidential information concerning participants in the process or operation."
I expect that 'such' refers to the confidential data or personal information.

(FR: "L'organisateur met en oevre ou il utilise telles données tandis qu'il est responsable du traîtement ou la préservation de l'information confidentielle en ce qui concerne les participants dans le processus de l'opération.")

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Note added at 2 days 10 hrs (2021-06-06 22:34:17 GMT)
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When reading about data or information, of a personal nature or 'character', the term 'data' with respect to personal information is unusual, though the French term literally translates as 'data'. The term 'data' would refer to information or statistics on more than one person, probably many people if it qualifies the use of 'data'. The treatment of data is likely to be about the storing of information on record and its safe-keeping. Information or 'data' is confidential when it's private or personal.
"There's the fundamental law which is in addition closely linked to the rightful respect of one's private life and family."

(FR: Tout en lisant sur des données ou des informations, d'un caractère personnel, l'usage du mot 'données' est insolite. Les données seraient des informations où des statistiques sur plus d'une personne, peut-être sur plusieurs, si ce sont des données. Le traîtement des données ou l'information personnelle est probablement sur le stockage, la conservation et la sauvegarde de celle-ci. L'information est confidentielle quand elle est privée.)
https://curia.europa.eu/jcms/upload/docs/application/pdf/201...
"Il existe le droit fondamental qui est en outre étroitement lié au droit au respect de la vie privée et familiale."

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Note added at 5 days (2021-06-10 08:15:46 GMT)
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"One datum is a single piece of information in the form of a fact or a statistic. The plural word term is 'data'. "
(Collins Gem English Dictiionary)
www.thefreedictionary.com/data
"Data are facts that can be analyzed or used in an effort to gain knowledge or make decisions. Data, the plural form of datum, are information. Data are statistics or other information represented in a form which is suitable for processing by computer."

(FR: 'Des données dont des faits qu'on peut analyser et qu'on peut utiliser dans les efforts ou les travaux pour gagner ou pour acquérir plus de connaissance. Des données, ou des dates, qui sont le pluriel d'un datum, sont des informations. Des données ou des dates sont des statistiques ou des autres informations representées d'une forme convenable ou appropriée au traîtement d'ordinateur.')

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Note added at 5 days (2021-06-10 09:53:33 GMT)
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The plural form has more than one or several items, objects or elements.
"Preservation is protection from harm or damage. Conservation is preservation such as protection, maintenance, custody, safeguards and upkeep."
https://www.thefreedictionary.com/conservation
"La forme plurielle comporte plus d'un objet ou élément ou plusieurs objets ou éléments.
La préservation est la protection contre du mal, des préjudices ou des dommages. La conservation est la préservation telle que la protection, l'entretien, le maintenant et le sauve-garde."