I missed a few chits while posting a group invoice. How do I merge 2 or more group invoices of the same company into 1 invoice?

Group invoice cannot be merged. 

Please delete the posted group invoice and remake them under 1 invoice.

1. Go to Invoice -> Group Invoice -> Posted Group Invoice.
2. Click View of the invoice you wish to delete.
3. Click Delete of any chit then the group invoice will be deleted as a whole. 
4. Remake the group invoice by including all the relevant chits.