Here is one example of how the Kotlin package does so:

https://github.com/andreypfau/ton-kotlin/blob/f0f2e7e05bc46d48fcbf6cef75249eea46890c7a/ton-block/src/commonMain/kotlin/org/ton/block/AddrStd.kt#L108

import org.ton.crypto.base64
import org.ton.crypto.base64url

fun convert(address: String): String {
	val raw = try {
			base64url(address)
	} catch (E: Exception) {
			base64(address)
	}
	return raw;
}