It is best that you show your dentist for this.
You can try these steps till you get to the dentist:
Take Tab. Motrin/Advil 400 mg twice daily for the pain, available over the counter
It is important to avoid biting the tissue. Take soft foods which require minimum of chewing
Do not touch the area, it will only cause more inflammation.
Rinse your mouth with warm saline water three-four times daily, this is very important to control inflammation. Water should be warm, not hot, and not too salty.
Apply Chlorhexidine ointment to the area after the rinse, many brands are available
If these steps do not help you need to show a dentist.
If you cannot get an early dental appointment, you should call 111. Ask for the dentist.
The dentist online will ask a few questions and give you a referral to the nearest Dental hospital or any other hospital with a dentist on call.
You will be able to get an emergency dentist appointment in this way.
You can also go to the nearest Urgent Care centre:
https://www.nhs.uk/service-search/other-services/Urgent-Care/LocationSearch/1824
Till you see the dentist, you should continue with the above steps which will help you.