New AST for tenants in situ and increase rent

Property Investment

Hi, I have recently completed on a property where the tenenat in situ's AST will expire soon in like 3 weeks. I would like to issue a new one for a number of reasons as the previous landlord has not done an inventory or put all the adults on the tenancy. At the same time I want to increase the rent slighty which is going to still be less than the market rent. I will speak to the tenent to come to a agreement on the rent increase. I want to find out what I need to serve and how to go about this. I searched for more information on this but I could not see what or how I can approch this. Thanks in advance for any help on this.