Hi, from this class, I'd like to modify the "MONTHLY"

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Hi, from this class, I'd like to modify the "MONTHLY"

and "ROI" strings from the GUI using a ComboBox? I've searched but couldn't find anything concrete.
Do you have any ideas?

using BasicProject.Model;
using Newtonsoft.Json;
using System.Collections.Generic;
using System.Net.Http;
using System.Threading.Tasks;

public class BinanceApi
{

public static async Task<List<UserRank>> GetLeaderboardRank(string tradeType)
{
try
{
using (HttpClient client = new HttpClient((HttpMessageHandler)new HttpClientHandler()
{
UseCookies = false
}))
{
string payload = JsonConvert.SerializeObject((object)new
{
tradeType = tradeType,
isShared = true,
isTrader = false,
periodType = "MONTHLY", // ALL, MONTHLY, WEEKLY, DAILY
statisticsType = "ROI" // ROI, PNL
});

}
return userRanks;
}
}
catch (Exception ex)
{
BinanceApi.Log.Error((object) ex);