Hello, there are many forums/sites that cover vehicle detailing (it’s an industry in itself now!) and soft tops in more detail than I can so I won’t restate at this time but have a look at a company called ‘Renovo’ who have been around awhile now.
I have used their soft top cleaner and dye with good success in the past. Works on targa panels too.
Their web site is helpful and details processes for soft top cleaning and preservation. I have only used ‘black’ version (kit of cleaner/proofer/dye) so cannot endorse their other products or newer interior products.
Looks bit costly on their web site – £63 for a full kit but often seen better offers in magazines etc. Think mine was <£40 but good few years ago! Expect maybe better pricing on eBay/amazon..

Alternatively you cannot go far wrong with Autoglym products, fair price & consistently good IMHO.

ahttp://www.renovointernational.com/

Let us know how you get on and what product you try.

Regards, Robin U.K.