Convert text form field to signature field

Hi, can someone tell me if there is an easy way to convert a column of text form fields to signature fields?

When running the "Prepare form" tool, it detects all the fields perfectly (3 columns of 45 rows each). However the middle column is intended for signatures, which is why I would like to know if it's possible to change all the rows in that column from text fields to signatures fields? 

I did consider to delete the detected fields in that middle column, and them manually insert a signature field in each, only that it would be quite time consuming.

I also tried to delete the detectec mid-column fields and then run the "prepare form" again, hoping that the auto-detect wizard would then detect them again as signature fields, but to no avail. I also couldn't seem to see if the auto-detect wizard can actually publish detected fields as other types of fields. Not sure if this is even possible?

Any help will be very much appreciated. Thank you