@Mohammed8 as posted Sjy do not allow accounts to be moved between people your sister will have to cancel and then you have to re-order.
It is a pain but unfortunately the only way round it is leaving the account in your sister's name get her to authorise you to be able to talk to Sky and the payment can come from your bank account which maybe worth doing if the service is still in the fixed 18 month contract period.
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65inch Sky Glass, 3 Sky Streaming Pucks, Sky Ultrafast + and Sky SR213(white Wifi Max hub) main Wifi from 3 TP-Link Deco M4 units in access point mode
