Suryanamaskar (12 mudras / exercise with integration of breath), if he can do, will help the person with low blood pressure.
Tadasana, talasana, katichakrasana, vakrasana, bhujangasana, shalabhasana, halasana in very slow manner would help in dealing with the low blood pressure.
Suryabedhan Pranayama and Kapalbhati Pranayam will also help.
Jala-mudra will also help. Touching the small finger with the thumb. It will help blood disorders. You can try for 15 minutes - each in morning, noon and evening.
Consulation with the doctor is necessary to cope with low blood pressure problem. The above points should not be treated as replacement of doctors' advice.