When you fill in the form for submitting papers, only the Abstract is allowed to have LaTeX macros and then only in mathematics mode. In other places, such as your name, enter special characters directly. You might find it convenient to copy-paste these:

ä Ä ë Ë ï Ï ö Ö ü Ü ÿ Ÿ

á Á ć Ć é É í Í ƙ ń Ń ó Ó ś Ś ú Ú ý Ý ź Ź

à À è È ò Ò ù Ù

ñ Ñ

â Â ê Ê î Î ô Ô û Û ŵ Ŵ ŷ Ŷ

ç Ç ȩ Ȩ ş Ş ƫ ţ Ţ

ą Ą ę Ę į Į ų Ų

å Å ů Ů

ā Ā ē Ē ī Ī ū Ū

ģ Ģ ķ Ķ ļ Ļ ņ Ņ ș Ș ț Ț

ő Ő ű Ű

ċ Ċ ė Ė ż Ż ġ Ġ İ

ă Ă ĕ Ĕ ğ Ğ ŏ Ŏ ŭ Ŭ z̆ Z̆

č Č ď Ď ě Ě ň Ň ř Ř š Š ť Ť ž Ž

æ Æ œ Œ ß đ Ð ø Ø ı ť Ł ł Ł þ

If you can't find what you need here, there are many larger tables on the internet, such as this one.