The back office "Keeper" can set scheduled visits at clients for the user or indicate weeks between visits for a user.
For individual updates. Simply go to Customers, select the customer, ensure the user is assigned to this customer.
On the left hand side you can click on the + to add a scheduled visit on a particular day or your can + a task to be done at this customer. On the right hand side within the customer details you can also select weeks between visit next to the user's name as indicated below:
Alternatively for bulk updates across your entire Customer database, go to Administration and Import visit frequencies and import tasks: