I was trying to do a backup from admin cp tools， but i keep seeing this memory size error

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 20480 bytes) in /home/dir/oc-includes/osclass/classes/database/DBRecordsetClass.php on line 186

how to fix it, if anyone has an experience.

thnx

@diverk
It was probably not possible to create backup using available memory.
For large sites, it's much more recommended to use hosting options for backups.