updating customer information from a list sharepoint

Hello.

I need advice on setting up my sharepoint management tool

I have two basic lists. One (list n° 1) where I record customer information (contact details). The other list (list n°2)  allows me to register the equipments. For each of the equipment in the list n° 2  is associated a user retrieved in the list n° 1 (by a search column ).

I have to follow the evolution of the attribution AND update the new users / . To do this, I was considering creating a list 3. This list 3 tracks assignment changes but I would need to use it to override the users informations from the equipment (list 2).

The methodology would therefore be :

1. create the new user in list 1 if it does not exist,
2. create a new item in list 3 and select the old user contact there, then the new user contact,
3. Update the new user in the list 2.

I would like to know if it is possible to do all this directly from list 3 and probably use power automate to

• check that the client already exists in list 1,
• if it exists do not create it. If it does not exist create it
• find the equipment in list 2 and update its user from list 3

Could you please help me on how to achieve this if possible. If not, what could possibly be done to meet my needs?