How to get "mentionSegmentInput.id" in Salesforce Chatter?

Hi,

I this code will explains thing you want -

List<AccountTeamMember> list_objAcctmem = [SELECT UserId, AccountId, IsDeleted, User.Name FROM AccountTeamMember WHERE AccountId =: objCase.AccountId LIMIT 25];
        ConnectApi.FeedItemInput feedItemInput = new ConnectApi.FeedItemInput();
        //ConnectApi.MentionSegmentInput mentionSegmentInput = new ConnectApi.MentionSegmentInput();
        ConnectApi.MessageBodyInput messageBodyInput = new ConnectApi.MessageBodyInput();
        ConnectApi.TextSegmentInput textSegmentInput = new ConnectApi.TextSegmentInput();
    
        messageBodyInput.messageSegments = new List<ConnectApi.MessageSegmentInput>();
    
        textSegmentInput.text = 'Casenumber ' +objCase.CaseNumber+' with the status '+objCase.Status+' has breached SLA aggrement hours';
        messageBodyInput.messageSegments.add(textSegmentInput);
        
        
        // Mention a group.
        if(list_objAcctmem.size() > 0)
            {                
                for(AccountTeamMember objAcctmem : list_objAcctmem )
                {
                    ConnectApi.MentionSegmentInput mentionSegmentInput = new ConnectApi.MentionSegmentInput();
                    mentionSegmentInput.id = objAcctmem.UserId;
                    messageBodyInput.messageSegments.add(mentionSegmentInput);
                }
            }
        feedItemInput.body = messageBodyInput;
        feedItemInput.feedElementType = ConnectApi.FeedElementType.FeedItem;
    
        // Use a record ID for the subject ID.
        feedItemInput.subjectId = objCase.Id;
    
        ConnectApi.FeedElement feedElement = ConnectApi.ChatterFeeds.postFeedElement(null, feedItemInput, null);

Hope this helps.