All right, so I added this to my function.php and it works fine. Thanks Shamim

function fep_remove_own_avatar() {
  $participants = fep_get_participants( get_the_ID() );
  if (($key = array_search(get_current_user_id(), $participants)) !== false) {
    unset($participants[$key]);
}
  $current_user = get_current_user_id();
  $count = 1;
  ?>
  <div class="fep-avatar-p <?php echo ( count( $participants ) > 2 ) ? 'fep-avatar-p-120' : 'fep-avatar-p-90' ?>"><?php
  foreach( $participants as $p ){
    $participant_id = fep_get_userdata( $p, 'ID', 'ID' );
    if( $count > 2 ){
      echo '<div class="fep-avatar-more-60" title="' . __('More users', 'front-end-pm') . '"></div>';
      break;
    }

    ?><div class="fep-avatar-<?php echo $count; ?> <?php if ( $participant_id === $current_user) { echo "fep-avatar-own";} ?>"><?php echo get_avatar( $p, 60, '', '', array( 'extra_attr'=> 'title="'. fep_get_userdata( $p, 'display_name', 'ID' ) . '"') ); ?></div><?php

    $count++;
  }
  echo '</div>';
}
add_action( 'fep_message_table_column_content_avatar', 'fep_remove_own_avatar' );