I’m sorry to say that in order to have your PIP claim looked at again given your worsening health, they’d have to look at the entire claim again.
It’s truly a horrible process, but there are ways of taking some of the stress out. First of all, try to get familiar with the different ‘descriptors’ and where you should be scoring points. In order to get your head around this, have a look at https://www.benefitsandwork.co.uk/ You could think about joining Benefits and Work. Or use the guide produced by the CAB: Personal Independence Payment - Citizens Advice You can see the rough guide to the points system here: https://www.citizensadvice.org.uk/Global/Migrated_Documents/adviceguide/pip-9-table-of-activities-descriptors-and-points.pdf
Then, start writing notes on your current care and mobility needs. Plus, begin collecting evidence to support what you will need to say. You should get letters from anyone who is familiar with your MS. So, your neurologist, MS nurse, carer(s), physiotherapist, other health professionals, even friends and family who help with your daily care needs. You can even include photos of the equipment and facilities you use at home (I had photos of my bathroom and bedroom showing the aids and adaptations I need).
Once you understand the points system, have a guide to each of the descriptors, have your own notes regarding your needs and some evidence to support your claim, you just need to get a change of circumstance form from the DWP and either complete it yourself, or get help to write it. Don’t forget that a welfare rights advisor can only use the information you give them, so the best quality information and evidence will improve your claim.
It’s a long slog and can be stressful, but the more organised you are, the better your claim will be and ultimately, the least stress you’ll experience!