In the operations tab, there are some things you could try to repair it.
If that don't work: Open your backup of the database.
If you have saved it as SQL statements, then you find a line with
CREATE TABLE IF NOT EXISTS `xoops_avatar` (
`avatar_id` mediumint(8) unsigned NOT NULL auto_increment,
`avatar_file` varchar(30) NOT NULL default '',
`avatar_name` varchar(100) NOT NULL default '',
`avatar_mimetype` varchar(30) NOT NULL default '',
`avatar_created` int(10) NOT NULL default '0',
`avatar_display` tinyint(1) unsigned NOT NULL default '0',
`avatar_weight` smallint(5) unsigned NOT NULL default '0',
`avatar_type` char(1) NOT NULL default '',
PRIMARY KEY (`avatar_id`),
KEY `avatar_type` (`avatar_type`,`avatar_display`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 ;
and then several
INSERT INTO `xoops_avatar` (`avatar_id`, `avatar_file`, `avatar_name`, `avatar_mimetype`, `avatar_created`, `avatar_display`, `avatar_weight`, `avatar_type`) VALUES
(1, 'cavt1234567891abc.jpg', 'Me', 'image/jpeg', 0, 1, 0, 'C'),
(2, 'cavt1234567890abc.jpg', 'You', 'image/jpeg', 0, 1, 0, 'C'),
....;
You can delete the avatar table by the command drop table in phpMyAdmin
Then you can copy above gathered lines into the window of the SQL tab and execute them.
This should restore your table.
Other possibility is to only empty the table and then doing only the inserts. But as the table itself is not recreated, it may have less chance to complete recovery.