Membership ver 3 crash

I just installed membership ver 3. Previously I had an earlier version, with some configuration done.

While I was in the admin doing some configuration changes to membership, I got a white screen. From that point on, none of my main site pages display, even the admin. However, the subsites are ok.

Renaming the membership directory on the server (just like removing it) fixes the issue.

How can I reset the tables in the database for the membership plugin, so I can start with a fresh install of ver 3 ?

Please help

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Additional info, somehow, the membership plugin got deactivated and was able to try to reactivate from the admin, and I got this error :

Fatal error: Cannot redeclare class paypalexpress in /var/www/vhosts/ressourcepro.com/httpdocs/wp-content/plugins/membership/membershipincludes/gateways/gateway.paypalexpress.php on line 892