In the tashahud after doing shahada of Prophet Muhammad (before Salwat) if I pause to think of my pronunciation and after a gap of pause I decide to repeat the recitation, do I just repeat that statement of Prophet shahada, or should I restart the tashahud recitation from start.

The reason I’m asking is because if I repeat just the one sentence of prophet shahada, the sentence starts with “wa ashhadu anna muhammadan…” – the “wa” means “and” which implies an extension of previous sentences. Since I’ve made a pause, does this sentence in its own suffice?

The question makes sense. There is no need to to start the tashahud afresh so long as the pause is not long. Repeating the statement suffices.