Restore a Zoho CRM back up into... Zoho CRM

Restore a Zoho CRM back up into... Zoho CRM

I used to manage all my contacts & opportunities with Zoho a few years ago. Before closing the account for a while, I had made a complete back up (10 USD) that left me with a data.zip containing in separate csv files all my data.
I would like to start a zoho crm account again.
I imagined that it was more than easy to make everything working again but so far i did not manage to.
Has anybody try this, to me, very common operation ?
Thanks for your help
Cheers
T