How to change all tags to hierarchy

Hello! I'm trying to add all my tags to another column for easier library tagging management, I'm able to move all my tags from one column to another, but I'm not able to convert the tags to a hierarchy, eg:

long, fantasy, favourite -> long.fantasy.favourite

I am trying to do this in bulk, but it appears like this:
[your test] fantasy, long, favourite -> fantasy.long.favourite
[book 1] fantasy, long, favourite -> fantasy ::: long ::: favourite

https://imgur.com/a/uptNBDO

Adding a \ before the comma doesn't help either. Any advice appreciated!! I have 0 programming knowledge whatsoever.