Discount

I’m currently biting my teeth on a way to allow the customer in a bill a discount in X%.
The field in the offer module is present or two, what is missing is the function that deducts and outputs the amount entered as a percentage of one field from the total amount.
Can anybody help me with this?
Say final amount - discount

Thank you so much for your help in advance.

Need more information
Are you using the Quotes or Invoices module?

Line items displays a discount field

Ich habe gesehen, dass Sie Deutsch sprechen. Ich such noch jemanden, der mir suite CRM an meine Bedürfnisse anpasst. Könnte ich Sie irgendwie erreichen?

VG

LC