Current Situation- Resource 1 is shared resource between Activity 1 and Activity 2. Here, the Resource 1 complete 1 work item in Activity 1 and moves to Activity 2. After that, Resource 1 complete 1 work item in Activity 2 and moves to Activity 1.
Required Modification - Resource 1 complete 5 work items in Activity 1 and moves to Activity 2. After that, Resource 1 complete 5 work items in Activity 2 and moves to Activity 1. However, this process should be continued throughout the whole simulation run.
If I understand the logic of your simulation correctly, it should work if you use (for both activities) Routing In > Collect 5 ("Do not collect until all available) and assign the resource as normal to both activities. Then, the resource will work until 5 work items are processed and only then will be released to go to the next/previous activity.
Hope this helps.