Hi can yo use wood platters that you use during the year if you only put cold items on them?
Yup
If they were used for hot can you dip wood platters to kosher them?
Wood utensils like wooden spoons that are used in hot pots can be kashered with hagalah.
Wood platters on the other hand even if used with hot foods, they’re only Keli Sheni and therefore no need to kasher. Clean them well.