Delegating Approvals with Approver Coverers in Jira Service Management
For Service Management Projects it is also possible to select an approver coverer.
When the rule goes into effect, the app will change the approver:
Immediately, in all existing issues in the approval process where the rule owner is currently appointed as an approver
For new issues where the rule owner is appointed as an approver.
When the rule expires, the original approver will be reinstated automatically.
Approver Field
The app supports approvers captured in either the native approver field, or in any additional custom field for approvals.
To select this, simply pick the relevant field in the dropdown.

Known Restrictions
JQL-based rules are not supported for approvers
Groups of approvers are not supported
Only a single approver coverer is supported.
Changes to the workflows governing the approval processes may result in the app not being able to delegate approvals for existing issues that went into the approval process before the last change to the workflow.
Out of Office Messages and Approver Coverers
It's possible to create rules without normal coverers and with only approval coverers.
However, note that in the case below:
the Out of Office message will not be shared when the app replaces an approver with their coverer.
the Out of Office message will be shared when an issue is assigned to the user that created the rule.
