Stagg is not a brand that is well considered. It’s generic for all sorts of instruments made in the far east and badged Stagg. For £150 look on the marketplace here for a brand that is a guitar maker. Many instruments are made by far east factories and then badged but QC by the brand.
Result, @Bef, did you get shown how to do this yourself? If not check YouTube for instructions as it may change when you put on new strings or sometimes with the weather. Adjusting the truss rod isn’t hard, take a look.