[Plugin: tags merge] need a little help

Hello,

I’m new to php language and I have a task to create wordpress plugin that would merge tags into one with a different name. Could someone please help me with this?
There are already plugins that do that and more, like:
https://github.com/scribu/wp-term-management-tools/blob/master/term-management-tools.php

But I would like to have much simpler version, that would only merge tags. I would greatly appreciate any help.