diff --git a/src/operations.js b/src/operations.js
index e20f759..7437efc 100644
--- a/src/operations.js
+++ b/src/operations.js
@@ -1,4 +1,5 @@
 import { removeStateLabels } from './labels.js';
+import { isPullRequest } from './pulls.js';
 
 /**
  *  By the document, we need remove & add assignees to replace them.
@@ -43,6 +44,44 @@ async function replaceAssignees(
     return changeAssign;
 }
 
+/**
+ * @param {import('@octokit/rest').Octokit} aOctoKit
+ * @param {string} owner
+ * @param {string} repo
+ * @param {number} issueNum
+ * @param {Array<string>} currentAssignees
+ * @param {Array<string>} nextAssignees
+ */
+async function replaceReviewRequests(
+    aOctoKit,
+    owner,
+    repo,
+    issueNum,
+    currentAssignees,
+    nextAssignees
+) {
+    if (currentAssignees.length > 0) {
+        await aOctoKit.pulls.removeRequestedReviewers({
+            owner,
+            repo,
+            // eslint-disable-next-line camelcase
+            pull_number: issueNum,
+            reviewers: currentAssignees
+        });
+        // TODO: assert return value
+    }
+
+    const changeAssign = await aOctoKit.pulls.requestReviewers({
+        owner,
+        repo,
+        // eslint-disable-next-line camelcase
+        pull_number: issueNum,
+        reviewers: nextAssignees
+    });
+
+    return changeAssign;
+}
+
 /**
  * @param {import('@octokit/rest').Octokit} aOctoKit
  * @param {string} repoName
@@ -88,7 +127,23 @@ export async function assignReviewer(
         nextAssignees
     );
 
-    await Promise.all([changeLabels, changeAssign]);
+    const issueIsPullRequest = await isPullRequest(
+        aOctoKit,
+        owner,
+        repo,
+        issueNum
+    );
+
+    const changeReviewer = issueIsPullRequest ? replaceReviewRequests(
+        aOctoKit,
+        owner,
+        repo,
+        issueNum,
+        currentAssignees,
+        nextAssignees,
+    ) : null;
+
+    await Promise.all([changeLabels, changeAssign, changeReviewer]);
 }
 
 /**
@@ -184,4 +239,4 @@ export async function rejectPullRequest(
     );
 
     await Promise.all([changeLabels, changeAssign]);
-}
\ No newline at end of file
+}
diff --git a/src/pulls.js b/src/pulls.js
new file mode 100644
index 0000000..6944e00
--- /dev/null
+++ b/src/pulls.js
@@ -0,0 +1,21 @@
+/**
+ * @param {import('@octokit/rest').Octokit} aOctoKit
+ * @param {string} owner
+ * @param {string} repo
+ * @param {number} issueOrPullNumber
+ * @return {Promise<boolean>}
+ */
+export async function isPullRequest(aOctoKit, owner, repo, issueOrPullNumber) {
+    try {
+        await aOctoKit.pulls.get({
+            owner,
+            repo,
+            // eslint-disable-next-line camelcase
+            pull_number: issueOrPullNumber,
+        });
+
+        return true;
+    } catch (_e) {
+        return false;
+    }
+}