How to activate sodium percarbonate powder?

Our washing machine doesn't have hot water, just warm (≈28-30°C). And I've searched that sodium percarbonate powder needs 40°C+ to activate, or otherwise at least to just melt it?

So my question is, if I fill my washing machine with warm water and just melt the sodium percarbonate powder in a pot of hot water first before mixing it with the warm water, will the sodium percarbonate still do its job?

Mainly, I have some bulky laundry that I want to really disinfect/whiten and I'm in a tight space with nowhere to handwash so washing machine's my only choice.

Another option is to soak it in a basin of hot water+sodium percarbonate. It's just that it's a second option cause I'm sure I'm gonna make a mess of myself and the bathroom cause the laundry's surely gonna be so heavy.