Besides @ged_hickman1’s suggestion, you could install the Roon Web Controller extension, either with or without the Roon Extension Manager. (I’ve found that using the Extension Manager makes dealing with extensions a bit easier.)
The Web Controller extension will allow you to use the old iPad as a somewhat basic Roon control point. The interface isn’t as slick as a bona fide Roon remote’s, and getting everything set up involves some geekiness, but it will get the job done.