Before you delete a VPC, you would like to check what this VPC currently being used.
When we use a VPC, then we will surely find some network interface and/or EC2 instances inside it. When we delete a VPC and these resources still exist in the VPC, we will get an error along with the name of the resource.
So, first, you can check the network interface page of EC2 console to find if there is an active network interface in a VPC which you are going to delete. Check with which resource that network interface is associated with like EC2 instance, Network load balancer, etc. If you don't need those resources, delete them followed by deletion of VPC.