Not able to change preferred currency for payments

[RipWatermelon]

i currently have 5 GBP in my account, but i also have 20 dollars in my account.

i want to send the 20 dollars to someone in britain without changing currencies.

but the problem is that when i try to send the money, it automatically chooses GBP and i have no way of changing the priority.

i tried converting the USD to GBP but when i click on the 3 dots absoloutely nothing happens.