Heel bone (calcaneus) has a pain. Should I stretch it?

Yes. You should ice it to and wear an arch support. An antiinflammatory is a good idea as well. Sounds like plantar fascitiis.
It would make. Sense to find out what the cause of the pain is prior to attempting any form of treatment. If it is plantar fasciitis or achilles tendonitis, stretching may help a little, but you may need more help than that. Have it examined.
Heel . As dr macy said , it makes much more sense to find the cause of the pain , then initiate treatment.