Advice needed

It looks horrible, and I can’t tell whether there is any structural failure. What particular issues do you want to address? What is your objective?

 

If you have the right tools you can remove a damaged brick and replace it. The tools can be hand ie hammers and chisels, or power eg SDS.

In an ideal world you find a matching brick but TBH anything would do here.

I think you should find somebody local who can check how serious the overall deterioration is.

 

If you just want to fill the space you could glue some bits of brick in place with mortar, or maybe even just fill the whole gap with mortar, but there is long-term deterioration which will need addressing at some time.

 

Is the other side neater and sound? I'm guessing this side was not seen or something and you are trying to make it cosmetically more presentable?

A stone repair mortar with a colour through it would build the brick back up and patch a few others, but you would still have all the snottery pointing.