Inside RStudio IDE, when cursor is on a function name, you can click on Code > Go to function definition or use Show source code F2 key shortcut to open the Function definition inside the IDE source pane. You can easily navigate through functions this way. See RStudio IDE cheatsheet.
Hope it helps.
Also, if your question's been answered (even by you!), would you mind choosing a solution? It helps other people see which questions still need help, or find solutions if they have similar problems. Here’s how to do it: