The bark is the protection of the tree. The tree also takes care of the bark care itself, so you really don't have to worry about it.
Seal damage with tree wax
If the bark is injured, the tree can become sick from pathogens, bacteria and pests. That is why you should seal damage - if it is very large - with tree wax. This at least ensures that pathogens can no longer penetrate the tree bark. As a rule, however, the tree or bark regenerates itself, so hardly anything needs to be done here.
Lichen and moss on the bark
Now it happens very often that trees on the bark, especially on the side facing the weather, have lichens and mosses. How about it If these growths are harmful, you may even take away nutrients or even oxygen from the tree - and how can you treat them?
The vegetation is not harmful
First of all: These growths are in no way harmful. They may not always be nice to look at, but they are not harmful. They even protect the tree or bark, which is why you shouldn't remove them. Many gardeners fiddle with brushes here, but this can lead to the bark being damaged and cracks forming - and the tree is again susceptible to pathogens. So: doing nothing is the best option.