Sure, there are two options for traveling from Bangkok to Surat Thani, including by train or bus.
By train: There are several trains per day from Bangkok's Hualamphong Train Station to Surat Thani Railway Station, which take around 12-13 hours.
By bus: There are also several bus options per day from Bangkok's Southern Bus Terminal to Surat Thani Bus Terminal, which take around 10-12 hours.
It is recommended that you check the availability and schedule of the different options to determine which one is best for you, and book your ticket in advance. Also it is always good to check the safety measures for covid-19 for each mode of transport.