Please see the FAQ: What's a reproducible example (`reprex`) and how do I do one? Using a reprex, complete with representative data will attract quicker and more answers. Without one it's hard to provide very specific guidance.
Section 11.3.2 of R for Data Science has a good explainer on string encoding and the use of flexible packages like readr to handle them. Be sure to check that the configuration of R if you are using it directly or the RStudio configuration is set to the UTF-8 default.