Guessing functionality is accessible when user wants to map fields from input module to fields in database table.
The functionality is available at the following location in the UI:
Open MariaDB Bulk Loader module > Field mapping tab > Custom mapping button window > Guess button

The following issues detected during testing:

1. If all fields, came from input module, have different names Guess functionality doesn't work even if database fields are the same number. User must map every field one by one which can be hard for tables with many columns. Expected for this case is that guess functionality will map fields according their appearance in the list. I.e. first field from input to the first field in the table. This will speed up the process a lot.

2. Only one field from input has different name.
User clicks Map all inputs button and all fields except one are mapped correctly.
User opens the Custom mapping and clicks Guess button there.
This action adds one of already automatically mapped fields. In my case this is the first field in the list. See the screenshot for situation after clicking the button several times. It is expected that if there is only one field left and user clicks guess button this field must be mapped.