According to https://www.vlkolinec.sk/en/informacie/doprava/ buses run upto the village car park from the main station but only during July and August. Or that a taxi should cost around €15 to €20. Instructions for walking and cycling are also provided.
Alternatively buses run to Ružomberok,Biely Potok,Do Uhliska which according to open street map is around a 25 minuet walk (uphill) from the train station. You can use CP Online to check times and prices. Local city bus route 4 and the longer distance bus to Liptovská Lúžna do the journey. Note that longer distances buses to Banská Bystrica pass through non-stop - they do though stop a short distance away at Ružomberok,Biely Potok,pri moste. If a journey planner tells you to change there I'd recommend checking as the bus you are changing onto will start from the railway station. The journey planner at CP Online seems to wrongly think that city bus 4 does not serve the railway station - you can view a summery of departures for this route here - it looks to leave the station at 37 minuets past the hour with an additional bus at 07 on some hours on weekdays, and at 37 minuets past the hour on odd numbered hours only on weekends. This page does not include the longer distance services on other routes. According to open street map data the walk from the Do Uhliska bus stop is the Vtáčí chodník - and signed with a white background and green backslash.
Finally Vlkolínec is also about a 25 minute walk from the top of the gondola at Malino Brdo. This is open and useable by pedestrians, although not year round it is open more frequently then just July and August. The path here is a lot flatter and also appears to be a more major route. I am unclear if there is a bus to the bottom of the gondola from Ružomberok - their website says at - here, here and here - that there are buses at least some of the year but they look to irregular & infrequent. If it is running it looks like they typically leave the railway station at 0800, 0845 and 1000. Return buses leaving at 1555 and 1635. Many of those contradict each other and/or are out of date, I have no idea what the current situation is. Alternatively the bottom station of the gondola is about a 25 minuet walk (again relatively flat) from Ružomberok-Rybárpole railway station. Note that this is not the main railway station in Ružomberok, and does not have a direct connection with Bratislava. An adult ticket for the gondola costs €8 1 way or €10 return - full prices are at: https://www.bikepark.sk/cennik/lanovka/ - there is also a €2 refundable deposit on the card which holds your ticket. This year during the summer season it is running: 5th June to 24th June & 6th September to 10th October - weekends and holidays only. With daily operation in-between. source