I know how to draw a text in a circle or semicircle shape but how we can change the perspective? I need it for an project in isometric view.
Text in Affinity Designer, if still live editable text, can be scaled, mirrored and skewed, but cannot be differentially scaled as you would need to create the illusion of linear perspective in a drawing.
If you were looking for perspective versus isometric, you can convert your text to curves, and once you convert the text to curves, you can manipulate individual anchor knots as you need to get the effect you want; it will, of course, no longer be live editable text.
You can take an Affinity Designer file and place it or open it in Affinity Photo, which has perspective warp and other warps, and achieve a simple and effective perspective effect that way too.
For classic isometry, as has been noted in a far more on-point answer from User287001, all you need do is skew your text the appropriate direction to get the results you will need - see User287001's excellent answer for details and workflow.