try{
        con2=[select Contact_Role__c from Contact where id = :app.Student_Alumni_Name__c];
        system.debug('con2---->'+con2);
    
        // Check to see if contact roll is null
        if(con2.Contact_Role__c == NULL)
        {
            con.Contact_Role__c = 'Applicant';
        }
        else
        {
            boolean applicantFound = false;
         
            string[] contactRoleList = con2.Contact_Role__c.split(';',0);
           
            for(String contactRole : contactRoleList)
            {
              
                if(contactRole == 'Applicant')
                {
                    applicantFound = true;
                }
            }
            
          
            if(applicantFound==false)
            {
              
                con.Contact_Role__c = con.Contact_Role__c+'; Applicant';
            }
        }
        update con;
    }catch(System.DmlException e){
        system.debug(LoggingLevel.INFO, 'Contact save failed - ' + e.getMessage() + ',' + e.getLineNumber());
        ApexPages.addMessage(new ApexPages.message(ApexPages.severity.ERROR, 'An unexpected error has occurred saving your application: ' + e.getLineNumber() + ',' + e.getMessage()));

I have this code in my apex class. here app is another object's reference.

While running the code, I am getting this error

"first error: INVALID_CROSS_REFERENCE_KEY, Can not select a person account: [AccountId]".

What shuld I do to remove this error. Thanks in advance. Any help much be appreciated.