Open the downloaded .rar or .7z file using WinRAR or 7-Zip. Do not simply drag the folder to your desktop. Extract directly to the OMSI 2 root folder, ensuring the folder structure matches.
Below, you'll find the download link for the IVECO Crossway LE V2, a popular and highly-regarded bus model for the OMSI 2 simulator.
: There is also a formal IVECO BUS Family Low Entry expansion available on Steam developed by Kescrole AddOns, which includes highly detailed versions of these buses. Essential Modifications & Enhancements