West Ham went 1-0 down on 25th minute away from home before Jahmal Hector-Ingram left to the 80th minute to bring it level.
Ten minutes later West Ham was were awarded a penalty after Jahmal Hector-Ingram was pushed over in the box and Martin Samuelsen stepped up to convert it to make it 2-1.
West Ham will face Newcastle United in the Play-off final at St James Park for a place in division one of what is now called Premier League two.
West Ham United: Spiegel, Knoyle, Akinola, Rice, Sylvestre, Makasi, Dobson, Kemp (Powell 72), Diangana (Hector-Ingram 72), Holland, Samuelsen.
Subs not used: Howes, Wells, Hannam. Goals: Hector-Ingram 80, Samuelsen 90+1