Please notice how an object derived from the nn.Module base class is instantiated and called.
import torch
import torch.nn as nn
 
from heinsen_routing import Routing

class GECorrection(nn.Module):

    def __init__(self, d_cov, d_inp, d_out, n_out):
        super().__init__()
        
        self.d_inp = d_inp # int value 
        self.d_out = d_out # int value 
        self.n_out = n_out # int value 
        self.d_cov = d_cov # int value 
      
        self.routings = nn.Sequential(Routing(d_cov=d_cov, d_inp=d_inp, d_out=d_out, n_out=n_out))
        #self.routings = Routing(d_cov = d_cov, d_inp = d_inp, d_out = d_out, n_out = n_out)
   
    def forward(self, a, mu):
        for Routing in self.routings:
            a, mu, sig2 = Routing(a, mu)

        return a, mu, sig2

a_inp = torch.randn(128,  29)       
mu_inp = torch.randn(128, 29, 8, 32)

myObject = GECorrection(8, 32, 32, 29)
a, mu, sig2 = myObject(a_inp, mu_inp)

This should work now.