I want to know if I can top up my energy online at home without visiting the shops?

I want to if I can top up my energy online.? at home without visiting the shops

This requires a smart meter in prepayment mode, and for your supplier to support it. Bulb do not yet support smart prepayment meters and so, even if you have one, you can’t top up online.

See here for advice from Bulb on how to topup whilst self-isolating.