The lever to switch from water out of the shower head to out of the big tap has come away. The lever looks like it should be screwed in, but it won't go. Any ideas how to put it back together please?

Is it a delta faucet?

Hi. I don't know what a delta tap is, but both hot and cold lead into one bigger outlet. Thanks for your help.

I think you would be best served hiring a pro to limit your liabilities.