Your question is confusing and doesn't contain enough information.
I can try to answer by making some assumptions, but I may have the premise wrong.
You want to edit the URL of a mux in an IPTV network [I presume one provided by a third party], but then you talk about FTP and some local directories - it is unclear what any of this has to do with the question.
To edit the URL you'll need to make a local copy, e.g.
wget -O Local.m3u8 http://address.of.iptv.network
Replace http://address.of.iptv.network with the address from the URL: field when you select 'edit' from Configuration > DVB Inputs > Networks
This will create a file Local.m3u8 which should contain the mux addresses which you can edit, you can also delete any channels you don't want.
Make sure you give Local.m3u8 permissions which will allow TVH to read it.
You can then add an IPTV network in TVH with the address file:///path/to/file/Local.m3u8
Caveats:
Some IPTV providers generate their muxes dynamically which may mean any copy you make will have a limited lifetime.
There may be some level of indirection in the network file - a mux entry may load another .m3u8, which may load another,
so you may have to follow the indirection to get to the bit you want to edit.
