My new tubeless tyres wont stay inflated
A reputable bike shop that did work on your bike with unsatisfactory results should make every effort to make it right at no additional cost to you.  If you have a receipt documenting the service and amount you paid, bring that and the bike along with you. Even if it's been a bit of time (a couple weeks to a month), it's perfectly legitimate to bring the situation to them and expect them to fix it.  Management--as well as a quality mechanic--would want to know (and correct) any problems resulting from their work.  It may be a situation where some product isn't working as expected, or perhaps a new mechanic needs more or different training. In any case, they need to be aware a problem exists in order to correct anything, and that's where you come in.
This is what I've taught my children:  when you purchased a product or service and that product is defective or the service incomplete or done poorly, you should make the store or responsible person aware of the defect or your disappointment in a polite and clearly stated summary of the problem. Conclude the summary with a sentence or two that definitively states your expectations. No one can meet your expectations if they are unaware of what they are. Having in your possession a receipt or other documentation that outlines the work performed helps to bolster the legitimacy of your claim, although absence of such things is not a reason to not stick up for yourself.
In your case, the question you've posed to Bicycle Stack Exchange would be alright at the bike shop. Add to it a sentence or two stating your expectations.
The advice in the comments above--especially trying to find where it's leaking with soap and water solution-- would be something you could do to show you've made some effort to help find the problem.  Marking any areas where you've noted air bubbles (using something impermanent like tape or chalk--just nothing that would mar the product in case they choose to take them back).  Should an employee of the shop refuse or in any way impede your expectations, politely request to visit with a manager on duty and again restate to him or her the clearly defined problem and your expectations.