Hello, welcome in the Community.
Your code becomes in general better readable when you enclose it with three backticks
(but here readability is no problem
)
I think the mai argument may help you:
set.seed(2020)
y.tr.ols = matrix(rnorm(230),nrow=23,ncol=10,byrow = T)
y.te.ols = matrix(rnorm(230),nrow=23,ncol=10,byrow = T)
par(mfrow=c(5,2),mai=c(0.1,0.1,0.1,0.1))
for (i in 1:10) {
plot(y.tr.ols[,i], y.te.ols[,i],pch=3)
}

Created on 2020-07-20 by the reprex package (v0.3.0)