To ensure that the Approvals app is pinned to the top of the app bar of the Teams client for all members of the Retail team, you need to create a custom app setup policy and assign it to the Retail team members. Here are the steps to follow:

Sign in to the Teams admin center with your admin credentials.

Go to Teams apps > Setup policies.

Select Add.

Provide a name and description for the policy, such as Retail App Policy.

Optionally, turn on User pinning to allow users to pin apps and change the order of the pinned apps.

Under Pinned apps, select Add apps.

Search for the Approvals app and add it to the list of pinned apps. You can also add other apps that you want to pin for the Retail team members.

Click Save to create the policy.

To assign the policy to the Retail team members, go to Users on the left menu and select the users that belong to the Retail team. You can use the filters or the search box to find them.

On the right pane, under Policies, select Edit next to App setup policy.

Choose the Retail App Policy from the drop-down list and click Apply.