I am trying to move opportunity related lsit from duplicate account to other account when a record is update with duplicate Account Name.Here i.e I have two records A and B so when i update name of Account "B" as "A" all opportunity relatedlist data should be moved from Old record A to newly updated record.
Here is my trigger everything look good but trigger is not working can anyone help me find the issue...

trigger MerageAccOpp on Account (after update) {

    if (trigger.isUpdate){
    
        List<Account> lst_acc;
        List<Opportunity> lst_opp;
        String nameaccount;
        Account a;
        for (Account accnew : Trigger.new){
            system.debug('Enetered');
            a=accnew;
         system.debug(a);

        }    
    
        nameaccount=a.Name;
// Here getting the duplicate account into list based on account name
        lst_acc=[select id,name from Account where name=:nameaccount and id!=:a.Id];
        system.debug(lst_acc);
        for(Integer i=0;i<=lst_acc.size()-1;i++){
// Condition to send duplicate account into "i"
            if(lst_acc[i].Id !=a.Id){
                system.debug('continue');
                system.debug(lst_acc[i].name);
                system.debug(lst_acc[i].Id);

//Getting opportunity of duplicate account into lst_opp based on duplicate account Id
     lst_opp=[select id,accountid from opportunity where AccountId=:lst_acc[i].Id];  
                system.debug(lst_opp);       
        
        if(lst_opp!= null){   
         system.debug('Enetered Opp Loop');
            for(Integer j=0;j<lst_opp.size();j++){
              lst_opp[j].AccountId=a.Id;  
                system.debug('AccountId changed');
                   update lst_opp[j];
                system.debug( lst_opp[j].AccountId); 
            }
         }   
         } 
        }                                            
    }
}
}