From the database click on settings.

You will be landed on the all unit page

Step 1:
Click on Invoice

Step 2:
Click on bulk action to reach the Bulk Action tab. you will be landed on the bulk action page. 

By using the filter option you can filter out the invoices and generate the next month's invoice for a single or multiple tenants.

Step 1:
Select the tenants

Step 2:
Hit on generate invoice will generate the next period invoice

Step 3:
Hit on export to export it as a pdf, Excel.