In the approval matrix you can specify rules that determine which Approvers will be selected for each particular request. They are based on the Requester/values in created custom fields.
Although positive rules are set by default, there is a way to add not only positive but also negative rules.
How to add a negative rule
In the main menu, go to your Organisation and open Approval workflows under Workflows and settings:
In the respective workflow, click on the approval matrix icon
Then click on the
icon next to the field you want to set.
In the drop-down menu, select "Does not match".
Save your changes by clicking on DONE.