Hi and welcome to HCM
Muscle strains & spasms will generally resolve spontaneously over a period of time.
Please follow the below mentioned general guidelines -
Stretching exercises of back, applying muscle relaxant
gel and doing hot fomatation will be helpful to relieve the spasm. You can take antiinflammatory drug like ibuprofen
to relieve pain and inflammation.
I do hope that you have found something helpful and informative and I will be glad to answer any further query.