By you, or whomever runs accounting for your company. The conversion doesn’t have to be an actual conversion, but you would use the rate for that day to do it. Again, this is for accounting and tax purposes, what you do with the cash may be different.
So for example, on June 1 you invoiced 10k EUR, but live in the UK, so technically, you’ve invoiced £xxx pounds which is what you’d report on your cash-flow statement.
I see your question now, the︀ answer is, you can whatever you want with the cash, but for tax and accounting︁ purposes you will want to convert the amounts into a single currency on paper.