https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/727420/T4_Migrant_Guidance_JULY_2018_FINAL.pdf

Tier 4 Policy Guidance version 07/2018 page 56 of 109

208. If you can show that you have already paid all or some of your
accommodation fees to your Tier 4 sponsor before making your application,
this amount, up to a maximum of £1,265, will also be taken away from the
total amount of money you will need to show for living costs. However,the
amount taken away cannot exceed a maximum of £1,265, even if you have
paid more than £1,265 in advance for accommodation (except if you are a
boarding student studying at a residential independent school).
For example, if you are studying in London, are studying a course of more
than 12 months, and you have paid your course fees in full, the amount of
maintenance you would need to show would be £11,385 (£1,265 for 9
months); however, if you have already paid £1,265 to your university as a
contribution towards your accommodation, the amount you need to show is
reduced to £10,120:
Amount of Maintenance - £11,385
Amount paid to Sponsor for accommodation - £1,265 Total
maintenance you are required to show - £10,120.

This only applies if you will be staying in university, college or independent
school arranged accommodation.

If you've arranged accommodation yourself you don't have to worry about that clause.