How to connect wirelessly music from computer /TV to external speaker like home theatre?

Sigh. In order to broadcast radio sound or receive radio broadcasts (which is what wireless means outside of cell phones) you have to have something with a radio broadcaster built into it and a receiver built into it. or connected up to it externally. If the manufacturer did not do this (which is most of them) then you don't get to do that. In any case the signal quality and sound quality is very poor. Not up to home audio standards. No one thats into sound music reproduction is going to extoll the virtues of what in hi fi terms is a piece of wax paper and a comb, .

Don't waste your time trying.

Use cables.

Because inexpensive, consumer grade wireless systems require the signal to pass through additional lossy compression/decompression steps, the sound quality is substantially compromised. It's counterproductive as heck.

Thus, at the current state of the technology, wireless continues to be a marketing gimmick designed for people who don't know any better, or who value convenience over sound quality (like for small portable speakers, or wireless headphones).