You might try to set the "Class name" to "User" to access this User (account) table, in properties table of rex_parse_itemtable plugin. After authenticated, you could read user ID by "Expression:UserID", it is equal to objectId in this table at the first field of each row.
Now you could
1. set the cash by "Action:Set value"
2. set the gunlevel by "Action:Set value"
3. set userID by "Action:Set itemID" ( userID = itemID = objectId )
4. call "Action:Save" to save this row into parse server, "Condition:On save complete" will be triggered while saving successful.