καὶ τἆλλα ὅσα δεῖ ἵπποις ἔχουσι χρῆσθαι.
The Latin translation provided by the comentary is :quae ubi equi habent, uti iis opportet. This ἔχουσι is a participle, right? Can we say: καὶ τἆλλα ὅσα δεῖ ἵπποις ἔχειν τοῦ χρῆσθαι?
It’s not surprising you find this difficult. It’s tricky, but very Greek in its syntax. Yes, εχουσι is the participle all right, agreeing with ιπποις, but your imaginary Greek sentence doesn’t work. The construction in Xenophon’s sentence is like e.g. (to simplify slightly) χαλινους δει ιπποις εχουσι χρησθαι, “one has to use horses having reins" (i.e. horses with reins), meaning horses have to have reins if you’re to make use of them. So here instead of e.g, χαλινους as the object of εχουσι (participle) we have ταλλα οσα, “everything else that (horses) have to (have).” So we end up with τἆλλα ὅσα δεῖ ἵπποις ἔχουσι χρῆσθαι. Straightforward enough once you sort it all out.
thank you it is clear now.