Source tax can only be reclaimed if a double taxation agreement between Switzerland and the new foreign domicile stipulates that this country taxes the pension capital.
It does not matter whether the source tax is higher or lower than the tax in the country of domicile. The source tax cannot be reclaimed if Switzerland taxes the pension capital in accordance with the tax agreement - or if there is no agreement at all. If the applicant can reclaim the source tax, the entire amount is usually refunded without interest.
To do so, they must submit the corresponding application to the tax office of the Canton of Schwyz within three years - you can find the form here: form source tax refund