A colleague sent me a .odt file so off I went looking for a viewer - and found the above

Having installed it - all my word documents have become Textmaker documents and I can't edit or even create new ones or word documents

Of course there is no uninstallicon with this damned program - can anyone help me?

I'm no techie either - so will need walking through it

Should be fairly straightforward. Right click on a word doc, select "open with", select "MSword", make sure that the checkbox "always use..." is ticked. You're good to go.
Open TMViewer. There should be file association options somewhere in the settings. Check that they are all unticked, except for the ones you want.
Someone else has had the same problem, even with those boxes unticked, so you're not alone.