D

#include <bits/stdc++.h>

using namespace std;

#define ll     long long
#define _test   int _TEST; cin>>_TEST; while(_TEST--)

int main()
{
    _test
    {
        int n, m;
        cin>>n>>m;

        vector<string> s(n);
        for(auto &e: s)
            cin>>e;

        int f = 0;

        for(int i=0; i<n; i++)
        {
            int cnt = 0;
            for(int j=0; j<m; j++)
                cnt += (s[i][j] != '.');

            f |= (cnt%2);
        }

        for(int j=0; j<m; j++)
        {
            int cnt = 0;
            for(int i=0; i<n; i++)
                cnt += (s[i][j] != '.');

            f |= (cnt%2);
        }

        if(f)
        {
            cout<<-1<<"\n";
            continue;
        }


        vector<vector<int>> ans(n, vector<int> (m, -1));

        for(int i=0; i<n-1; i++)
        {
            int c = 0;

            for(int j=0; j<m; j++)
            {
                if(s[i][j]=='U')
                {
                    ans[i][j] = c;
                    ans[i+1][j] = c^1;
                    c ^= 1;
                }
            }
        }

        for(int j=0; j<m-1; j++)
        {
            int c = 0;

            for(int i=0; i<n; i++)
            {
                if(s[i][j]=='L')
                {
                    ans[i][j] = c;
                    ans[i][j+1] = c^1;
                    c ^= 1;
                }
            }
        }

        for(int i=0; i<n; i++)
        {
            for(int j=0; j<m; j++)
            {
                if(ans[i][j] == -1)     cout<<'.';
                if(ans[i][j] ==  1)     cout<<'B';
                if(ans[i][j] ==  0)     cout<<'W';
            }
            cout<<"\n";
        }
    }
}