How do I get more concurrent automation workers available for my plan if I run out?

You can purchase additional automation workers at any time using one of the paid subscription plans. The additional automation workers can be purchased via your JetBrains Account.  

1 Automation worker costs $35 per month.

To see the prices in other currencies, please refer to the pricing page. The base price is shown in US dollars. Prices in other currencies are provided for reference and are calculated based on the approximate conversion rate. The final price will be provided at the checkout, and it may differ from the reference prices due to the current currency conversion rates used by JetBrains.

You cannot purchase additional automation workers on the Free plan.