You can use endorse contacts campaign to automatically endorse upto top three skills of your existing 1st degree connections. Follow the below steps to create an endorse campaign:
1. Search 1st connections.
Paste your search url from Linkedin or Sales navigator and hit search.
2. Save your search results by clicking the gear icon.
4. Name your search and click save.
5. Click Add New campaign
6. Enter your campaign details
Input campaign name, select "endorse contacts" as campaign type and select prospects from the dropdown. Save & continue.
7. Input your campaign setting and schedule. Save & continue.
8. Review your setup and settings
Click the + button. If everything seems alright, click Send campaign.