I've made a reservation for London Bloomsbury and on the app there is a Guest requests button. I have about a dozen reservations live but only this one has the guest request option.

On it is the following options.

The option to advise the hotel if you are arriving before 3pm or after 10pm

Pillow preference - the options are no preference or hypoallergenic

Elevator preference - near or far away from the elevator

Floor location - high, low or ground

Request a crib

Request a rollaway bed

Request extra pillows

The usual blurb about preferences not being guaranteed and are based on availability is mentioned along with a charge possibly applying for additional extras.