As a general rule don't source any information from TikTok. That influencer is either lying or not following safety guidelines from the manufacturer.
The GP is highly unlikely to prescribe, even if they could they'd make you go through two tiers of weight loss methods before offering medication, so diet advice, maybe weight watchers type courses and so on. The tier 3 approach on the NHS could be injections but in many areas is bariatric surgery instead.
Private prescriptions can be prescribed by online pharmacies. The pharmacy should be GPhC registered, you can find comparison lists from a couple of websites that are updated frequently:
www.missmounjarouk.com
monj.co.uk
Privately via these pharmacies you can choose between Wegovy (semaglutide) or Mounjaro (tirzepatide). Mounjaro is newer and research shows it produces greater weight loss with fewer side effects than Wegovy (also called Ozempic).
Both medications are similar, they are called GLP-1 receptor agonists. They mimic what happens to your body when you eat, which normally wears off in a few minutes. These artificial versions last for a week or so. They produce a feeling of fullness, and so reduce appetite and feelings of wanting to over eat. You feel fuller quicker and on less food. They also slow down your digestive transit. That can lead to side effects for some people, can be nausea, constipation, diarrhoea, vomiting. Usually only temporary and can be sorted out with changing diet, OTC treatments or if necessary reducing the dose that you're on.
These medications are meant to be taken long term. A pen contains four doses which you take once a week, so it lasts for a month. The first month of Mounjaro is a dose of 2.5mg each week which is meant to get your body used to the medication. Many people don't experience weight loss on this dose. After 4 weeks you can move up to 5mg which may start to produce weight loss. Then you can move up if you feel you need to, in steps of 2.5mg until you reach the maximum dose of 15mg which is the highest dose you can take.
A Mounjaro pen has to be discarded 30 days after you take the first dose.
The websites I linked have details of discount codes and referral codes which you can use to get a cheaper price. You can change suppliers whenever you want, to take advantage of the new customer discounts. The only issue might come when your BMI is less than 30 as a new prescriber may be reluctant to take you on as you wouldn't meet their prescribing criteria.