Alter (verb): to make different in some particular, as size, style, course, or the like; modify

“But just how a visit to a park or other green space might alter mood has been unclear. Does experiencing nature actually change our brains in some way that affects our emotional health?” How walking in nature changes the brain by  GRETCHEN REYNOLDS

As I was reading this short paragraph, the word ALTER stopped me from reading further down. Alter sounds familiar but the spelling of it does not exist in my memories. Looking it up after trying to make a guess gives me a better understanding. I realized I’ve heard this word when my friends and I went to get their clothes altered. The reason why the word is familiar yet strange to me is that I’ve never bothered to look up for the spelling of it. “But just how a visit to a park or other green space might change the mood has been unclear.”