PHP wrap xml value with tag

How to replace CJ value which is in second last line with :

         <rank>CJ</rank> 

and save the updated xml file.

<MLRAU_2018_121>
<OTHER_CITATIONS>
<ILJ_CITATION></ILJ_CITATION>
<MLJ_CITATION></MLJ_CITATION>
<MLJU_CITATION>MLJU_2018_50</MLJU_CITATION>
<ILR_CITATION>ILR_2018_1_433</ILR_CITATION>
<CLJ_CITATION>CLJ_2018_2_513</CLJ_CITATION>
<LNS_CITATION>LNS_2018_1_36</LNS_CITATION>
<AMR_CITATION></AMR_CITATION>
</OTHER_CITATIONS>

<REPORTED_CITATION></REPORTED_CITATION>

<JUDGMENT_COUNTRY>CANADA</JUDGMENT_COUNTRY>
<JUDGMENT_LANGUAGE>ENGLISH</JUDGMENT_LANGUAGE>

<JUDGMENT_NAME>Hash SALES &amp; SERVICES (M) limited v. John </JUDGMENT_NAME>
    <COURT_TYPE>High Court Toronto &amp; Some Name</COURT_TYPE>
<JUDGE_NAME><NAME>Jay</NAME> CJ, <NAME>Sonac</NAME>, <NAME>Prasad Sandosham</NAME>, <NAME>Jeffrey Tan</NAME>, <NAME>Khar</NAME> FCJJ</JUDGE_NAME>
</MLRAU_2018_121>

via Chebli Mohamed