I'm a third party who need to submit data to Zoho CRM owned by Organization A through API.

Referring to your guideline mentioned here :  https://www.zoho.com/crm/help/api/v2/#oauth-request

 who should do the registration? is it me (third party) or Organization A  (owner and  Zoho CRM account admin).

Do they need to perform all the steps or only Step 1 - Step 2?