I have two custom object. 
One is student_Master__c. Field is: Name,Pancard Number,Phone, Background Check Status.
and another is Black_Listed_candidate__c. Field is: Name, PAN, phone.

Condition: Whenever we are inserting record in student_Master__c it has to check "pancard number" in above database. If the "PAN number" is found in "Black_Listed_candidate__c" object, then show message in "Background Check Status" field that "candidate is blacklisted. we cannot hire!."
 And also as well as update "Phone" field in "Black_Listed_candidate__c" object record with new phone present in "student_Master__c" object record.

Please help me with this. I am trying but give error.

This is my code below:

Apex Class:

public class PancardCheckClass {
   @future 
    public static void updateBlackListPhone(Map<Id,string> idAndPhoneMap)
    {
        list<Black_Listed_Candidate__c> blackListedPans = [SELECT Name,PAN__c,Phone__c FROM Black_Listed_Candidate__c WHERE Id IN:idAndPhoneMap.KeySet()];
        for(Black_Listed_Candidate__c black :blackListedPans)
        {
            black.Phone__c = idAndPhoneMap.get(black.Id);
        }
        Update blackListedPans;
    }    
}

Trigger:

trigger PancardCheckClassTrigger on Student_Master__c (before insert) {
    
    list<Black_Listed_Candidate__c> blackList =[SELECT Name,PAN__c,Phone__c FROM Black_Listed_Candidate__c];
    system.debug('kdng' + blackList);
    list<Student_Master__c> newRecord = new list<Student_Master__c>();
    Map<Id,string> IdAndBlackListPhoneMap = New Map<Id,string>();
    
    for(Student_Master__c varStudent: trigger.new)
    {
        for(Black_Listed_Candidate__c varBlacklist:blackList)
        {
            if(varBlacklist.PAN__c==varStudent.Pan_Card_Number__c)
            {
                varBlacklist.Phone__c=varStudent.Phone__c;
                IdAndBlackListPhoneMap.put(varBlacklist.Id, varBlacklist.Phone__c);
                newRecord.add(varStudent);
            }
        }
        if(newRecord.size() > 0)
        {
            PancardCheckClass.updateBlackListPhone(IdAndBlackListPhoneMap);
            for(Student_Master__c newAppRecord : newRecord)
            {
                newAppRecord.Background_Check_Status__c='Candidate is Blacklisted! We cannot hire!';
            }
        }
    }
    
}