Apart from properties that are exempt from business rates, each non-domestic property has a rateable value which is set by the Valuation Office Agency (VOA), an agency of Her Majesty's Revenue and Customs. They compile and maintain a full list of all rateable values, available at Gov.UK - VOA. The rateable value of your property is shown on the front of your bill. This broadly represents the yearly rent the property could have been let for on the open market on a particular date specified in legislation. For the current rating list, this date was set as 1 April 2021.
The VOA may alter the valuation if circumstances change. The ratepayer (and certain others who have an interest in the property) can also check and challenge the valuation shown in the list if they believe it is wrong.
Further information about the grounds on which challenges may be made and the process for doing so can be obtained by contacting the VOA, or by consulting the VOA website: Gov.UK - check your rateable value.