are you talking about a situation where a client comes to the gym to train with you and you are aware that they have high blood pressure?
Somebody with high blood pressure should be under a physician’s supervision, and the blood pressure should be controlled through one of more medications so that it falls into the normal range. Clients with high blood pressure usually check their blood pressure regularly to make sure that it is still normal. If your client does not do it and you suspect that their blood pressure readings are in the ‘high’ range, then you should take their blood pressure before the start of training. If it is too high, do not train the client and send him/her back to the doctor asking for another clearance to exercise even if you had one before.
You can advise your client to walk in the meantime and to check the blood pressure frequently.
Uncontrolled high blood pressure must be addressed before training can resume. You can ask for exercise parameters from the doctor as far as frequency, intensity and duration once it resumes.