There is an equivalent to "se promener" in English: we often translate it with the phrase "go for a walk" (in British English) or "take a walk" (in American English). Like "se promener', this phrase implies that you're walking relatively slowly, for recreational purposes,: for pleasure or gentle exercise. In the future, we might say "I'm going to go for a walk in the city centre"; in the past, we'd say "I went for a walk in the city centre" - or perhaps "round the city centre".

I’m going to take a walk downtown / around the city centre. I took a walk downtown/ around the city centre.

I am not French, I am English , but I speak French, Thai and Arabic too I think that marcher=promener In that they both mean walking Would you agree? Or do you think there’s a slight difference ?

I’m going to have a walk around the city center...

Bonjour , I walked around the city center. I'm going for a walk in the city center.