Common Selfheal can be propagated by division into new individual plants.
Check to see if there is more than one plant. In some cases they may still be beneath the soil surface. If you feel confident, you may remove the soil to check for baby plantlets below!
If there are multiple plants growing, unpot the plant and gently tug the plants apart, being careful not to disturb too many of the roots. They may be connected by large root segments which you may need to break to free the plantlet.
Pot up the new plant in well-draining soil
Repot the parent plant back into its original pot