All parts (part01, part02, etc.) must be in the same folder. Extracting part01 will usually combine them into a single file (often named MstarUpgrade.bin or similar).
Downloading firmware from unofficial sources (like multi-part .rar files from forums) carries risks, including system instability or "bricking" your TV. The safest way to obtain the correct software is through official channels: Download RT2861V09 3840x2160 16G Kivi 49UP50GU part08 rar
Do you have the of your KIVI TV to verify if this is the correct version for your specific hardware? Software - KIVI All parts (part01, part02, etc
Searching for the specific file name suggests you are looking for a multi-part firmware archive for a KIVI 49UP50GU All parts (part01